Disposable pillars for contact formation

ABSTRACT

Sacrificial plugs for forming contacts in integrated circuits, as well as methods of forming connections in integrated circuit arrays are disclosed. Various pattern transfer and etching steps can be used to create densely-packed features and the connections between features. A sacrificial material can be patterned in a continuous zig-zag line pattern that crosses word lines. Planarization can create parallelogram-shaped blocks of material that can overlie active areas to form sacrificial plugs, which can be replaced with conductive material to form contacts.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/282,671, which is a continuation of U.S. patent application Ser. No.12/170,786 filed Jul. 10, 2008, which is a divisional of U.S. patentapplication Ser. No. 11/217,980 filed Sep. 1, 2005 (now U.S. Pat. No.7,399,671).

This application is related to pending U.S. patent application Ser. No.10/690,317, filed Oct. 20, 2003, entitled FORMATION OF SELF-ALIGNEDCONTACT PLUGS, the entirety of which is hereby incorporated by referenceand made part of this specification.

BACKGROUND OF THE INVENTIONS

1. Field of the Inventions

The disclosed inventions relate generally to integrated circuitfabrication, techniques for fabrication of computer memory, and contactformation therefor.

2. Description of the Related Art

As a consequence of many factors, including demands for increasedportability, computing power, memory capacity, and energy efficiency inmodern electronics, integrated circuits are continuously being reducedin size. To facilitate these size reductions, the sizes of theconstituent features, such as electrical devices and interconnect linewidths, that form the integrated circuits, are also constantly beingdecreased.

The trend of decreasing feature size is most evident in memory circuitsor devices, such as dynamic random access memories (DRAMs), staticrandom access memories (SRAMs), ferroelectric (FE) memories, etc. Totake one example, DRAM typically comprises millions of identical circuitelements, known as memory cells.

By decreasing the sizes of constituent electrical devices and theconducting lines that access them, the sizes of the memory devicesincorporating these features can be decreased. Storage capacities for agiven chip area can thus be increased by fitting more memory cells ontomemory devices without increasing the overall size of the devices.

The continual reduction in feature size places ever greater demands onthe techniques used to form the features. One well-known technique isphotolithography, commonly used to pattern features, such as conductivelines, on a substrate. The concept of pitch can be used to describe thesize of these features. For the repeating patterns typical of memoryarrays, pitch is defined as the distance between an identical point intwo neighboring features. Adjacent features are typically separated by amaterial, such as an insulator. As a result, pitch can be viewed as thesum of the width of the feature and of the width of the space ormaterial separating that feature from a neighboring feature. Due tooptical factors, such as lens limitations and light or radiationwavelength, photolithographic techniques have minimum pitches belowwhich a particular photolithographic technique cannot reliably formfeatures. This minimum pitch is commonly referred to by a variabledefining one half of the minimum pitch, or feature size F. This variableis often referred to as a “resolution.” The minimum pitch definable byphotolithography, 2F, places a theoretical limit on feature sizereduction.

One method for improving the density possible using conventionalphotolithographic techniques is to change the layout of a memory devicein order to fit more memory cells in the same area without changing thepitch. Using such a method, the size of the memory device can be reducedwithout exceeding the minimum pitch, 2F, dictated by opticallimitations. Alternatively, the memory device may be configured to holdmore memory cells, while maintaining a constant pitch.

Memory layout changes, particularly those accompanied by increasedfeature density, and other factors have contributed to the need forimproved subcomponent configurations and methods for formingsubcomponents that are adapted to the memory layout changes.

SUMMARY OF THE INVENTIONS

Some embodiments comprise a method of forming an integrated circuithaving multiple levels. The method can comprise the following steps:providing active areas; providing a plurality of word lines above theactive areas; coating the word lines with a sacrificial material;patterning the sacrificial material in a first pattern having continuouslines and removing intervening portions of the sacrificial material thatare not part of the first pattern; coating the patterned sacrificialmaterial with an insulating material; planarizing the insulatingmaterial down to a first plane to expose portions of the sacrificialmaterial; removing the exposed portions of the sacrificial material toleave voids; depositing a conductive material into the voids; andplanarizing the conductive material to leave isolated plugs within thevoids.

Some embodiments comprise an integrated circuit that includes aplurality of conductive plugs for use in an integrated circuit. Theconductive plugs can comprise blocks of conductive material with anonrectangular, parallelogram footprint, flanked on first and secondopposite sides by two word lines and flanked on second and thirdopposite sides by blocks of insulating material, the blocks ofconductive material being configured to contact underlying active areasand provide an electrical connection with an overlying bit line. Theblocks of conductive material in the integrated circuit can beassociated with a plan view pattern, the pattern comprising thefollowing portions: first columns, each first column comprising a wordline; second columns alternating regularly with the first columns, eachsecond column comprising the box of conductive material, which alternateup and down the column with blocks of insulating material, the secondcolumns arranged in ascending and descending trios. The ascending trioscan comprise three sequential second columns having blocks of conductivematerial with parallelogram footprints, each parallelogram footprinthaving a top edge parallel to a bottom edge wherein the top and bottomedges of parallelogram slope upwardly to the right, and each top edge isaligned with the top edge of two other blocks of conductive material inother second columns in the ascending trios. The descending trios cancomprise three sequential second columns having blocks of conductivematerial with parallelogram footprints, each parallelogram footprinthaving a top edge parallel to a bottom edge, wherein the top and bottomedges of the parallelogram slope downwardly to the right, and each topedge is aligned with the top edge of two other blocks of conductivematerial in other second columns in the descending trios.

Some embodiments comprise a memory device having a first componentgrouping. As seen in plan view, the first component grouping cancomprise: a first elongate active area defining a first axis, the firstactive area comprising a first source and at least first and seconddrains; at least two substantially parallel word lines that cross andoverly the first active area, at least a portion of a first word linelocated between the first drain and to the first source, at least aportion of a second word line located between the second drain and thefirst source; and a first plurality of contact plugs on the samevertical level as the word lines, the contact plugs comprising rhomboidportions of conductive material the first plurality of contact plugscontacting and generally overlying the first active area, at least oneof the first plurality of contact plugs extending between the at leasttwo word lines and at least one of the first plurality of contact plugsextending outwardly from either word line, each of the first pluralityof contact plugs being aligned with the first axis.

Some embodiments comprise a method of forming conductive plugs for acomputer memory array. The methods can comprise patterning a sacrificialmaterial in continuous lines that cross word lines. The method canfurther comprise filling spaces between the sacrificial material andword lines with insulating material. The method can further compriseremoving the sacrificial material to form plug voids, the plug voidsbeing separated by word lines in one dimension and separated by theinsulating material in another dimension. The method can furthercomprise filling the plug voids with conductive material to formconductive plugs. Some embodiments comprise a method of manufacturing aportion of the memory device. The method can include providing asubstrate and a defining an elongate active area within the substrate,the axis of elongation of the active area defining a first axis. Themethod can further comprise defining at least one pair of word linesthat define a second axis, the second axis crossing the first axis at anangle in a range of approximately 20 to approximately 80 degrees.Moreover, the method can comprise filling a space between the word linesand over the active area with a sacrificial material. The method canalso comprise removing the sacrificial material and replacing it with aconductive material to form a conductive contact, the conductivematerial having two sides that are parallel to the first axis and twosides that are parallel to the second axis.

Some embodiments comprise a method of forming conductive plugs betweentransistor gates. The method can comprise patterning a sacrificialmaterial in continuous zig-zag (in plan view) lines. The zig-zag lineshaving thinner (in cross-section) bridge portions that cross thetransistor gates and thicker fill portions that fill the space betweenthe gates. The method can further comprise removing at least the thickerfill portions to form voids with sidewalls formed from insulatingmaterial. The method, moreover, can comprise filling the voids withconductive material to form conductive plugs.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventions will be better understood from the Detailed Descriptionof the Preferred Embodiments and from the appended drawings, which aremeant to illustrate and not to limit the inventions, and wherein:

FIGS. 1A-1B schematically show two levels of an integrated circuit. FIG.1A shows a plan view of a level with oval-shaped active areas. FIG. 1Bshows a plan view of a level with word lines that overlie the activeareas of FIG. 1A. FIG. 1B also shows (in phantom) where curved bit linescan be positioned relative to the structure of FIG. 1B.

FIG. 2A and subsequent plan views show a close-up view of a smallerportion of the structure than is depicted in the plan views of FIGS.1A-1B, with selected underlying structure shown in phantom. In FIG. 2Aand subsequent figures, the overlying lines are not depicted.

In FIGS. 2-12, the same structure is depicted in each of the schematicillustrations associated with a particular figure. Thus, FIGS. 2A-2Cdepict various views or sections of the same structure, FIGS. 3A-3Cdepict different views or sections of the same structure, etc.Furthermore, the letter labels of sub-figures indicate consistent views.Thus, FIGS. 2A, 3A, 4A, etc. each show schematic plan views; ifunderlying structure is depicted, it is shown in phantom. FIGS. 2B, 3B,4B, etc. show schematic, cross-sectional side views. (The cross sectionof FIG. 2B is taken along lines 2B-2B of FIG. 2A, FIG. 3B shows a crosssection taken along lines 3B-3B of FIG. 3A, etc.) Similarly, FIGS. 2C,3C, 4C, etc. show schematic, cross-sectional side views taken alonglines C-C of the corresponding Figure A.

FIGS. 2A-2C show the structure of two levels of an integrated circuit(including active areas in a first level and word lines in a secondlevel) after coating the structure with a sacrificial material (e.g.,photoresist and/or conformal amorphous carbon).

FIGS. 3A-3C show the structure of FIGS. 2A-2C after the sacrificialmaterial of FIGS. 2A-2C has been patterned and partially removed,leaving behind lines of sacrificial material that cross portions of theword lines (shown in phantom) and that generally overlie the activeareas (shown in phantom).

FIGS. 4A-4C show the structure of FIGS. 3A-3C after coating thestructure with an insulating material (e.g., spin-on dielectric, or SOD)that fills in spaces between the lines of sacrificial material.

FIGS. 5A-5D show the structure of FIGS. 4A-4C after planarizing theinsulating material and the sacrificial material down to the top of theword lines.

FIGS. 6A-6C show the structure of FIGS. 5A-5D after selectively removingthe remaining portions of the sacrificial material.

FIGS. 7A-7D show the structure of FIGS. 6A-6C after coating thatstructure with a conductive material (e.g., silicon) that fills in thevoids left by removal of the sacrificial material.

FIGS. 8A-8D show the structure of FIGS. 7A-7D after planarizing theconductive material down to the top of the word lines.

FIGS. 9-12 show an alternative to FIGS. 5-8 that can be used to achievethe same structure depicted in FIGS. 8A-8C.

FIGS. 9A-9C show the structure of FIGS. 4A-4C after planarizing theinsulating material down to the top of the sacrificial material.

FIGS. 10A-10C show the structure of FIGS. 9A-9C after removing theremaining portions of the sacrificial material.

FIGS. 11A-11D show the structure of FIGS. 10A-10C after coating thatstructure with a conductive material (e.g., silicon) that fills in thevoids left by removal of the sacrificial material.

FIGS. 12A-12D show the structure of FIGS. 11A-11D after planarizing theconductive material and the insulating material down to a plane thatcorresponds to the top of the word lines.

FIG. 13 shows a schematic, cross-sectional view of a bi-cell transistorconfiguration incorporating the structure of FIGS. 12A-12D.

FIG. 14 shows a schematic plan view of a portion of an integratedcircuit incorporating the structure illustrated in FIGS. 8 and 12, andalso shows (in phantom) where curved bit lines can later be positionedto overlie that structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1A, active areas 32 are schematically illustrated,forming a pattern in an active area level 30. In the illustratedembodiment, a pair of memory cells comprises three electrical devices:two storage capacitors and an access field effect transistor having asingle source shared by the memory cells, two gates, two channels, andtwo drains. The pair of memory cells, therefore, has two addressablelocations that can each store one bit (binary digit) of data. A bit canbe written to one of the cells' locations through the transistor andread by sensing charge on the drain electrode from the source electrodesite. In some embodiments, rows 36 of oval-shaped active areas 32 form azig-zag pattern. From left to right across a row 36, the right-hand tipof each active area in a zig-zag row is near the left-hand tip of thesubsequent active area in the zig-zag row. In the illustratedembodiment, the elongate axes of each of the oval active areas 32 in aparticular row 36 are not aligned, but instead differ by an angle φ.Some embodiments have a symmetrical zig-zag pattern in that eachsuccessive intersection of elongate axes in a particular row 36 differsby the same angle φ. The angle φ can be in a range of approximately 45degrees to approximately 179 degrees, for example. Preferably, the angleφ is approximately 130 degrees.

In some embodiments, columns 38 of oval-shaped active areas 32 do nothave a zig-zag pattern. Thus, the elongate axes of each of the ovalactive areas 32 in a particular column 38 can be parallel, as shown.Thus, the repeating pattern of active areas can have a successive rows36 of zig-zag lines that form a hound's tooth or herringbone pattern.The zig-zag configuration can have two slopes that intersect at an anglein a range of between 45 and 179 degrees, for example.

The active areas 32 are formed in a semiconductor material such assilicon. The active areas 32 are doped regions of a semiconductorsubstrate as shown in various cross-sectional views (see, e.g., FIG.2B). The active areas 32 can be portions of a conductively doped siliconwafer that forms a substrate for an integrated circuit. The raisedactive areas 32 are surrounded in the same vertical level by insulatingmaterial or field isolation regions 34, which can be field oxide orshallow trench isolation material, for example.

In some embodiments, the active areas 32 comprise different regions thathave different properties from one another. For example, the differentregions can have different conductive properties. In the illustratedembodiments, each active area comprises a source region, as well as twochannel regions and two drain regions. For an illustration of wherethese regions can be located within the active area 32, see FIG. 13. Thesilicon in the various regions of the active area can be dopeddifferently. For example, in some preferred embodiments, the silicon inthe source and drain regions has been heavily doped (e.g., n+), whereasthe silicon in the channel regions has been less heavily doped withopposite conductivity type (e.g., p−). FIG. 13 shows how the source anddrain regions can be oriented in the active area 32 with respect toother structures in an integrated circuit.

Referring to FIG. 1B, word lines 42 are schematically illustrated asstripes that cross the active areas 32 in an overlying word line level.The word lines 42 overlie the active areas 32, and each active area 32contacts two word lines 42. In particular, the word lines 42 preferablycontact the active area 32 in the channel regions of the active areas 32(see FIG. 13). As can be understood from the cross-sectional viewsdiscussed below, the word lines 42 define insulated transistor gateelectrodes where they cross the active areas 32. Thus, the active areas32 can create an electrical connection between two insulated transistorgate electrodes, or word lines 42. The word lines 42 are separated byspaces 44, and the word lines 42 comprise multiple layers and/orportions that are illustrated in FIG. 2B.

As shown in FIG. 1B, the overlying bit lines 52 can be configured tocross over the central regions of the active areas 32. The centralregions of the active areas 32 can correspond to the source regions ofthe active areas 32. The source regions can connect with the overlyingbit lines 52 through bit line contacts 62. In the illustratedembodiment, spaces 54 between bit lines 52 cross over the peripheralregions of the active areas 32, which can correspond to the drainregions of the active areas 32. Cell contacts 64 connect the drainregions to memory storage devices (not shown), such as capacitors. Asused in this specification, the term “bit line” also encompasses thestructure sometimes referred to as a “digit line.”

Referring to FIG. 2A, a sacrificial material 220 has been deposited overthe word lines 42 and the active areas 32, which are both shown inphantom. The sacrificial material 220 fills the spaces 44 between wordlines 42, and thus portions of the sacrificial material 220 occupy thesame vertical level as a word line level. In preferred embodiments, thesacrificial material 220 is photoresist or conformal amorphous carbon.These materials are advantageous because they can be removed with highselectivity, as discussed further below. The sacrificial material 220preferably coats the word lines 42, and it is shown as a planarizedlayer in FIG. 2B. However, the layer 220 need not be smooth orplanarized because a later CMP step will be used.

Referring to FIG. 2B, the sacrificial material 220, word lines 42,active areas 32, and insulating material or field isolation regions 34are shown in cross section. The word lines 42 comprise multiple layeredportions, including a gate dielectric portion 230, a first conductiveportion 240, a second conductive portion 250, and an insulating capportion 260. The gate dielectric portion 230 can extend across the wholeactive area at this stage. As illustrated, the word lines 42 areinsulated from surrounding materials both by the insulating cap portions260 and by word line spacers 280. The gate dielectric portions 230 canbe formed from silicon oxide or high k materials such as Ta₂O₅, HfO₂ orZrO₂. The first conductive portions can 240 can be formed from polysilicon, metal silicide, or newer materials and metal compounds withtailored work functions. The second conductive portions 250 can beformed from metal silicide, elemental metals and metal compounds withhigher conductivity. The insulating cap portions 260 and the word linespacers 280 can be formed from silicon nitride, silicon oxide or similardielectrics. As shown in FIG. 2B, the active areas 32 can be raisedplateau portions of an underlying semiconductor substrate 210. Theactive areas 32 can have substantially vertical walls 236 that definethe boundary between the active areas 32 and the insulating material orfield isolation regions 34. Alternatively, the walls 236 can be slopedas shown.

Referring to FIG. 2C, a cross section taken along lines 2C-2C shows adifferent perspective of the layered configuration of the partly-formedintegrated circuit.

Referring to FIG. 3A, the sacrificial material 220 has been patterned ina continuous wavy line or zig-zag pattern such that portions of thesacrificial material 220 are intact over each row 36 (FIG. 1A) of activeareas 32. The lines of sacrificial material 220 generally follow thecontours of successive oval-shaped active areas 32 (shown in phantom),extending the length of one active area 32, bridging to cover anotheractive area 32, bridging to cover yet another active area 32, and soforth from left to right in the illustrated view. As illustrated, thelines of sacrificial material 220 cross over portions of the word lines42 as well as the spaces 44 (FIG. 1B) between word lines.

The pattern of continuous zig-zag lines of sacrificial material caneffectively overlie the various active areas 32, having similar anglesand intersecting elongate axes in a way similar to the above descriptionof the rows 36 of active areas 32 (see FIG. 1). In particular, eachzig-zag row of sacrificial material can overlie a row 36 of active areas32.

Because the elongate axes of a particular column 38 (see FIG. 1A) ofoval active areas 32 are aligned or parallel, successive zig-zag rows 36of active areas can form a hound's tooth pattern as discussed above withrespect to FIG. 1A. Furthermore, the zig-zag rows of patternedsacrificial material generally overlie the rows 36 of active areas 32.Thus, the zig-zag lines of patterned sacrificial material do not overlapwith each other and have zig-zag lines of space in between them. Theillustrated embodiment has a constant separation distance between eachzig-zag line. In some embodiments, the continuous wavy lines intersectthe word lines 42 at an angle between 10 and 80 degrees. For example, inFIG. 3A, one of the wavy zig-zag lines intersects one of the word lines42 at an angle α. In some embodiments, the angle α is the same as anangle β. Such a symmetrical configuration can make it easier to patternlarge arrays of structures such as those described herein. In someembodiments, the angle φ is twice the angle α.

Patterning the sacrificial material 220 in a continuous line can providehigher resolution than would otherwise be possible with a moredisjointed pattern having discreet elements (not shown). The sacrificialmaterial 220 can be patterned through a photolithographic process. Forexample, if the sacrificial material 220 is photoresist, conventionalphotolithography can be used. In some embodiments, where the sacrificialmaterial 220 is amorphous carbon, for example, a dry develop etchprocess can be used to pattern the sacrificial material 220. Inparticular, a dry develop process can involve dry-developing the resistand removing material that is not protected by the resist, thenstripping the resist pattern to leave behind lines of amorphous carbonover the active areas.

With continued reference to FIG. 3A, after the zig-zag pattern ofsacrificial material 220 has been formed and portions of the sacrificialmaterial coating have been removed as shown, there are voids 330 in thespaces 44 (FIG. 1B) between word lines 42, and the voids 330 are flankedabove and below (in plan view) by the thicker portions 320 of the linesof sacrificial material 220. (The lines of sacrificial material alsohave thinner portions 340, where the lines cross over the word lines42). Thus, the sacrificial material 220 has been patterned in a patternhaving continuous lines, and the portions of intervening sacrificialmaterial that are not part of the pattern have been removed.

Referring to FIG. 3B, which shows a cross section of the structureillustrated in FIG. 3A, the lines of sacrificial material 220 havethicker portions 320 in between the word lines 42 and thinner portions340 as the sacrificial material 220 crosses over the top of the wordlines 42. Furthermore, FIG. 3B illustrates the wordline spacers 280 thatprovide insulating material between the inner portions of the wordlines42 and the materials external to the wordlines 42. In particular, thewordline spacers 280 flank the left and right sides (in plan view) ofthe voids 330. Thus, the voids 330 are surrounded by four insulatingside walls, two formed from the thicker portions 320 and two formed fromthe wordline spacers 280.

Referring to FIG. 3C, the illustrated cross section is taken along oneof the word lines 42, and thus shows two thinner portions 340 ofsacrificial material 220.

Referring to FIG. 4A, a coating of insulating material 420 has beenapplied to the structure of FIGS. 3A-3C. The insulating material 420 hasfilled in the voids 330 (FIG. 3A). The insulating material 420 is deepenough, in the depicted embodiment, to cover all the structure of FIGS.3A-3C. The insulating material 420 can be a spin-on dielectric (SOD).The insulating material 420 can be densified at this point, or later asindicated below.

Referring to the cross-sectional views of FIGS. 4B and 4C, theinsulating material 420 is shown covering the sacrificial material 220.

Referring to FIG. 5A, both the sacrificial material 220 and theinsulating material 420 have been planarized (if not already planar) andetched back. In the illustrated embodiment, both materials have beenremoved generally down to a plane that corresponds to the top of theword lines 42. The remaining portions of the sacrificial material 220form pillars 520. The pillars 520 are defined and surrounded by the wordlines 42 to the left and right (in FIG. 5A), and by insulating material420 to the top and bottom (in FIG. 5A). The pillars 520 haveparallelogram “footprints.” Preferably, the pillars 520 have rhomboidalfootprints. As used herein, a footprint refers to an object's shape whenit is seen from a top or bottom plan view, for example when across-section of the object is taken along a plane parallel to the planof the plan view of FIG. 5A, for example. In the illustrated embodiment,the pillars 520 have parallelogram, rhomboid footprints as seen in theplan view, each parallelogram having an interior angle α′ thatcorresponds to the angle α. The angle α′ is an interior angle of therhomboid represented by the footprint of the pillar 520. The angles α′and α are preferably in a range between 10 and 80 degrees. Thus, in theillustrated embodiment of FIG. 5A, the parallelograms arenon-rectangular. In particular, the illustrated parallelograms arerhomboids.

Referring to FIG. 5B-5D, planarization has removed the thinner portions340 (FIG. 3B) of the sacrificial material 220, but left the pillars 520(corresponding to the thicker portions 320 of FIG. 3B) that are locatedin between the word lines 42 generally intact. The pillars 520 generallyoverlie portions of the active areas 32, as illustrated by FIG. 5D.Planarization can be accomplished using an etch step with a mechanicalcomponent, such a chemical mechanical polishing (CMP) etch. Otherprocesses that can be used to planarize include selective dry etch backprocesses. In a preferred embodiment, CMP is used and when the CMPreaches the level of the insulating cap portions 260 of the word lines42, the CMP is halted. Because the insulating cap portions 260 can beformed from nitride, CMP can be referred to as a “stop-on nitride” (orSON) process. Alternatively, the described CMP etch can be referred toas a SON CMP etch.

Referring to FIG. 6A, the sacrificial material 220 that remained afterplanarization has been removed, leaving plug voids 620 in between wordlines 42. In the spaces 44 (FIG. 1B), remaining portions of insulatingmaterial 420 form periodic blocks of material that alternate with theplug voids 620. The plug voids 620 leave portions of the active areas 32exposed. The plug voids 620 can have the same shape and anglecharacteristics of the removed pillars 520 (FIGS. 5A-5D) of sacrificialmaterial. For example, in the illustrated embodiment, the plug voids 620have parallelogram footprints as seen in the plan view, eachparallelogram having an interior angle α′ that corresponds to the angleα. The angle α′ is an interior angle of the parallelogram represented bythe footprint of the void 620. The angles α′ and a are preferably in arange between approximately 10 and approximately 80 degrees. Thus, inthe illustrated embodiment of FIG. 6A, the parallelograms arenon-rectangular. In particular, the parallelograms are preferablyrhomboids.

The sacrificial material 220 can be removed by a selective etch step.For example, if the sacrificial material 220 is photoresist, an oxygenplasma etch can be used. If the sacrificial material 220 is amorphouscarbon, a similar or sulfur/oxygen plasma can be used. If the remaininginsulating material has not already been densified, it can be densifiedafter the sacrificial material 220 has been removed as illustrated.

Referring to FIG. 6B, in the illustrated cross section, thefree-standing word lines 42 alternate with plug voids 620. The back wallof the insulating material 420 is omitted to more clearly illustrate thevoids 1020.

Referring to FIG. 6C, the cross-section taken along the word line 42 isunchanged from the structure shown in FIG. 5C.

Referring to FIG. 7A, the structure of FIG. 6A has been coated with aconductive material 720, which has filled the plug voids 620 left byremoval of the sacrificial material 220. The conductive material 720 canbe silicon, polysilicon, metal, tungsten, titanium, or a laminatedconductor, for example. In some embodiments, polysilicon is preferredbecause it can withstand processing temperatures. In the illustratedembodiment, the conductive material 720 forms the plugs that fill theplug voids 620.

Referring to FIGS. 7B and 7C, cross-sectional views of the conductivematerial 720 overlying the structure of FIGS. 6B and 6C are shown.Referring to FIG. 7D, a cross sectional view taken along the line 7D-7Dof FIG. 7A is shown.

Referring to FIG. 8A, the conductive material 720 has been planarizedsuch that all material above a plane generally corresponding to the topof the word lines 42 has been removed. Etch back processes or CMP, asdescribed above with respect to FIGS. 5A-5D, can also be used to achievethe structure illustrated in FIGS. 8A-8D. The planarization has createdplugs 820 from the conductive material 720. The conductive plugs 820 canfill the role of bit line contacts (see bit line contacts 62 in FIG. 1Babove) or cell contacts (see cell contacts 64 in FIG. 1B above),depending on their position with respect to an underlying active area32. The conductive plugs 820 form conductive contacts with theunderlying active areas 32 by passing down between the word lines 42. Byremoving the sacrificial material 220 to form the voids 620 (FIGS.6A-6B), the plugs 820 can be formed by coating the structure andplanarizing, as shown. Furthermore, the conductive plugs 820 areself-aligned in that the voids allow the conductive material 720 to fillin to form plugs 820 that are directly aligned with the underlyingactive areas 32 and do not require a mask step after depositing theconductive material. As described above with respect to the pillars 520of sacrificial material 220 and the voids 620, in the illustratedembodiment, the plugs 820 can have parallelogram (e.g., rhomboid)footprints as seen in the plan view, each parallelogram having aninterior angle α′ that corresponds to the angle α. The angle α′ is aninterior angle of the parallelogram represented by the footprint of thepillar 520. The angles α′ and α are preferably in a range between 10 and80 degrees. In particular, the parallelograms are preferably rhomboids.

As seen in the plan view of FIG. 8A, the illustrated plugs 820 have anon-rectangular parallelogram footprint. In the illustrated embodiment,the opposing top and bottom sides of each plug 820 are either ascendingfrom right to left, as with the plugs 820 overlying the central activearea 32 in FIG. 8A, or they are descending from right to left, as is thecase with some of the plugs 820 which are only partially visible in FIG.8A. For example, if the word lines 42 form columns (in plan view) asillustrated in FIG. 8A, the lines 42 alternate with columns 830 formedfrom the plugs 820 and blocks of insulating material with complementaryshapes, the two parallelogram (or rhomboid) blocks alternating in astriped pattern in the columns 830 up and down (in the view of FIG. 8A)between word lines 42. As illustrated, the angles of the stripes in thecolumns formed between word lines 42 corresponds to the angle of theelongate axis of the underlying active areas 32. In particular, threestriped columns 830 and two word lines 42 cross each active area 32. Thestriped columns 830 are grouped in ascending trios where they crossactive areas 32 that slope upwardly to the right, and in descendingtrios where they cross active areas 32 that slope downwardly to theright.

Referring to FIGS. 8B-8D, the cross sectional views show how the planeof planarization corresponds to the top of the word lines 42. Theillustrated planarization can be achieved using an etch step with amechanical components, such as chemical mechanical polishing. Otherprocesses that can be used to planarize include a selective dry etch ora non-selective dry etch timed to stop after reaching the top of theword lines 42 or otherwise configured (e.g., with optical end pointdetection) to end after exposure of the insulating caps 260. Asillustrated by FIG. 8D, the plugs 820 generally overlie the active areas32. The two plugs 820 illustrated in FIG. 8D can function as cellcontacts because they overlie the end regions of the active areas 32. InFIG. 8D, the side wall of the wordline 42 that would otherwise bevisible in such a cross-sectional view has been omitted to more clearlyillustrate the lack of structure between the plugs 820 along the column830 (FIG. 8A).

FIGS. 9-12 show an alternative embodiment to that described in FIGS.5-8. Indeed, the two alternative processes can be used to achievesimilar structure, as shown by FIGS. 8 and 12.

Referring to FIG. 9A, the insulating material 420 of FIGS. 4A-4C hasbeen planarized. In this embodiment, the insulating material 420 hasbeen removed generally down to a plane that corresponds to the top ofthe sacrificial material 220 above the insulator word line. Becauseplanarization has been stopped earlier than the step described at FIG. 5above, this etch step leaves intact the thicker portions of theinsulating material 420 and the sacrificial material 220.

Referring to FIGS. 9B and 9C, planarization has left intact the thinnerportions 340 of the sacrificial material 220, in contrast to theplanarization illustrated in FIGS. 5B and 5C, which removed the thinnerportions 340. As can be seen from FIG. 9C, the thinner portions 340 ofsacrificial material 220 are interspersed between thin portions 940 ofinsulating material 420, which also crosses the word lines 42.

Planarization can be accomplished using an etch step with a mechanicalcomponent, such as chemical mechanical polishing. Other processes thatcan be used to planarize include dry etching timed or otherwiseconfigured (e.g. by optical endpoint detection) to stop on thesacrificial material 220.

Referring to FIG. 10A, the sacrificial material 220 that remained afterplanarization has been removed, leaving deep plug voids 1020 bordered bythe word lines 42 and the wavy lines of insulating material 420. Thedeep plug voids 1020 are different from the plug voids 620 illustratedin FIG. 6 because the insulating material that forms two walls of eachvoid is taller for the deep plug voids 1020 in FIG. 10A. However, theword lines 42 that form the other two walls of each void are the sameheight for the plug voids 620 and the deep plug voids 1020. Furthermore,despite their differences, the deep plug voids 1020 leave portions ofthe active areas 32 exposed, just as did the plug voids 620 illustratedin FIG. 6.

The sacrificial material 220 can be removed by a selective etch step.For example, if the sacrificial material 220 is photoresist, a drydevelop or oxygen plasma etch can be used. If the sacrificial material220 is amorphous carbon, an oxygen plasma or SO₂-based plasma can beused.

If the remaining insulating material 420 has not already been densified,it can be densified after the sacrificial material 220 has been removedas illustrated. In some embodiments, densified material can be easier toremove than nondensified material. In some embodiments that usephotoresist (as the sacrificial material 220) and SOD (as the insulatingmaterial 420), densification at this point is advantageous becausephotoresist may not be able to withstand the cure temperatures of SOD.In some embodiments, furthermore, even if amorphous carbon is used asthe sacrificial material 220, that amorphous carbon may not be able towithstand some temperatures (e.g., in a range of approximately 500 to600 degrees Celsius). In this case, removing all of the sacrificialmaterial 220 before densification of the insulating material 420 (e.g.,of SOD) can allow for higher curing temperatures and/or longer curetimes, providing more processing flexibility.

Referring to FIG. 10B, in the illustrated cross section, thefree-standing word lines 42 alternate with plug voids 1020. The backwall of the insulating material 420 is omitted to more clearlyillustrate the voids 1020.

Referring to FIG. 10C, the cross-section taken along the word line 42illustrates that removal of the sacrificial material has resulted in theabsence of the thinner portions 340 of sacrificial material 220, butthat the thin portions 940 of insulating material 420 are still in placegenerally on the word lines 42 where they cross the insulating materialor field isolation regions 34.

Referring to FIG. 11A, a coating of conductive material 1120 has beenadded to the structure illustrated in FIG. 10A. The conductive material1120 has filled the deep plug voids 1020 left by removal of thesacrificial material 220. The conductive material 1120 can be silicon,tungsten or any other suitable plug material. In the illustratedembodiment, the conductive material 1120 forms the plugs that fill theplug voids 1020.

Referring to FIGS. 11B and 11C, cross-sectional views are shown of theconductive material 1120 that overlies the structure of FIGS. 10B and10C. Referring to FIG. 11D, a cross sectional view is shown taken alonglines 11D-11D of FIG. 11A.

Referring to FIG. 12A, the conductive material 1120 has been planarizedsuch that all material above a plane generally corresponding to the topof the word lines 42 has been removed. The planarizing processesdescribed above with respect to FIGS. 5A-5C and 8A-8C can also be usedto achieve the illustrated structure. The planarization has createdisolated plugs 1220 from the interconnected conductive material 1120.The conductive plugs 1220 form a conductive contact with the activeareas 32 underlying the word lines 42. The conductive plugs 1220 can actas bit line contacts (see bit line contacts 62 in FIG. 1B above) or cellcontacts (see cell contacts 64 in FIG. 1B above), depending on theirposition with respect to and underlying active area 32. By removing thesacrificial material 220 to form the deep voids 1020, the plugs 1220 canbe easily formed by simply coating the structure and planarizing, asshown. Furthermore, the conductive plugs 1220 are self-aligned in thatthe deep voids 1020 allow the conductive material 1120 to fill in andform the plugs 1220 that are directly aligned with the underlying activeareas 32 without a mask step. The conductive plugs 1220 can bestructurally identical to the conductive plugs 820 of FIG. 8.

Referring to FIGS. 12B-12D, the cross sectional views show how the planeof planarization corresponds to the top of the word lines 42. Theillustrated planarization can be achieved using an etch step with amechanical component, such as chemical mechanical polishing. Otherprocesses that can be used to planarize include dry etching. Asillustrated by FIG. 12D, the plugs 1220 generally overlie the activeareas 32. The two plugs 1220 illustrated in FIG. 8D can function as cellcontacts because they overlie the end regions of the active areas 32. InFIG. 12D, as in FIG. 8D, the side wall of the wordline 42 that wouldotherwise be visible in such a cross-sectional view has been omitted tomore clearly illustrate the lack of structure between the plugs 1220.

Referring to FIG. 13, the schematic, cross-sectional view illustrates anembodiment of an electronic device with which the structure of FIGS.12A-12C can be used. In particular, a first capacitor 1320 overlies twoof the word lines 42 at the left of the figure, and a second capacitor1330 overlies two of the word lines 42 at the right of the figure. Eachcapacitor has a top electrode 1324 and a bottom electrode 1328. The topelectrode 1324 can be a continuous common layer for an entire array,with periodic holes formed to allow the passage of structures such asthe bit line contact 1340, for example. In between the electrodes 1324and 1328 is a capacitor dielectric material 1326. In between the twocapacitors 1320 and 1330, a bit line plug 1340 forms an electricalcontact between a conductive plug 1220 and an overlying bit line 52. Asource region 1360 of the active area 32 is located below a conductiveplug 1220 in the central region of the active area 32. On either side ofthe active area 1360 are channel regions 1380. The tips of the activearea 32 have drain regions 1370, such that the channel regions 1380 canprovide a connection between the source region 1360 and the drainregions 1370.

In operation, electrical current can travel along the bit line 52, downthe bit line plug 1340, and into the source region 1360. Then, if theappropriate voltage is applied to the first conductive portions 240 ofthe word lines 42 and the appropriate charge carriers populate thechannel regions 1380, current can flow from the source region 1360 tothe drain regions 1370. The word lines 42 can act as “gates” because thefield generated by the first conductive portions 240 attracts electricalcarriers to the gate dielectric 230 and allows current to flow throughthe channel regions 1380. When the gate is “open,” allowing current toflow through the channel region 1380, an inversion layer of chargecarriers (either holes or electrons) is formed in the channel region1380. After flowing across the channel regions 1380, the current canthen flow through the two side conductive plugs 1220 and across theintermediate contacts 1390 to the two bottom electrodes 1328 forstorage. The intermediate contacts can be formed from a conductivematerial (e.g., polysilicon or metal). The described current flow canalso happen in reverse to drain the stored charge from the capacitors1320 and 1330. In this configuration, the outermost word lines 42 can beinactive.

Referring to FIG. 14, the schematic plan view illustrates a layout for aportion of an integrated circuit similar to the layout of FIG. 1B.However, FIG. 14 includes exemplary plugs 820 such as those illustratedin FIGS. 8A and 12A (1220). The plugs 820 are illustrated along with theunderlying active areas 32 and the overlying bit lines 52 to show howthe plugs 820 can help connect the source regions 1360 of the activeareas 32 to the overlying bit lines 52.

As shown in FIG. 14, the plugs 820 can be grouped according to whetherthey have top and bottom (in the plan view of FIG. 14) borders thatslope upwardly or downwardly. In particular, the memory device cancomprise a first component grouping that has a first elongate activearea defining a first axis. The first axis can slope upwardly to theright, for example, in the illustrated plan view. The first elongateactive area can have a first source and first and second drains. Thedrains can be located toward the tips of the oval-shaped active area,while the source can be located toward the center of the active area.The first component grouping can further comprise two substantiallyparallel word lines that cross and overlie the first active area, and atleast a portion of a first word line can be located between the firstdrain and the first source. The first component grouping can furthercomprise a first plurality of contact plugs located on the same verticallevel as the word lines. The contact plugs can comprise parallelogram(or rhomboid) portions of conductive material. The plurality of contactplugs can generally contact and overlie the first active area. At leastone of the first plurality of contact plugs can extend between the atleast two word lines and at least one of the first plurality of contactplugs can extend outwardly to the right and left from either wordline.The first plurality of contact plugs is preferably aligned with thefirst axis, as illustrated.

A second component grouping can be described similarly to the firstcomponent grouping, but with an axis that slopes downwardly to theright. Several groupings that meet the descriptions of first and secondcomponent groupings are illustrated in FIG. 14. Furthermore, the slopesof the first and second axes can have the same magnitude but oppositedirection, as illustrated. (See FIG. 1A for an illustration of exemplaryelongate axes of active areas).

The structure, principles and advantages discussed herein are applicableto a variety of contexts in which sacrificial plugs are formed inconnection with features of an array. Accordingly, it will beappreciated by those skilled in the art that various other omissions,additions and modifications may be made to the methods and structuresdescribed above without departing from the scope of the invention. Allsuch modifications and changes are intended to fall within the scope ofthe inventions, as defined by the appended claims.

We claim:
 1. An integrated circuit comprising: a plurality of wordlines; a plurality of conductive plugs comprising, as seen in plan view,blocks of conductive material with a nonrectangular, parallelogramfootprint, the blocks of conductive material flanked on a first pair ofopposite sides by two of the word lines and flanked on a second pair ofopposite sides by blocks of insulating material; a plurality of memorystorage devices overlying the conductive plugs; and a plurality ofactive areas underlying the conductive plugs, wherein each of theplurality of memory storage devices is contacted by a block ofconductive material so as to provide an electrical connection to atleast one of the active areas.
 2. The integrated circuit of claim 1,wherein the non-rectangular, parallelogram footprint is a rhomboidfootprint.
 3. The integrated circuit of claim 1, wherein thenon-rectangular, parallelogram footprint has at least two interiorangles of between approximately 20 and approximately 30 degrees.
 4. Theintegrated circuit of claim 1, wherein the non-rectangular,parallelogram footprint has at least two interior angles of betweenapproximately 40 and approximately 50 degrees.
 5. The integrated circuitof claim 1, wherein the blocks of conductive material are associatedwith a plan view pattern, the pattern comprising: first columns, eachfirst column comprising one of the word lines; second columnsalternating regularly with the first columns, each second columncomprising the blocks of conductive material, which alternate up anddown each of the second columns with the blocks of insulating material,the second columns arranged in ascending and descending trios, wherein:the ascending trios each comprise three sequential second columns havingblocks of conductive material with parallelogram footprints, eachparallelogram footprint having a top edge parallel to a bottom edge,wherein the top and bottom edges of the parallelogram slope upwardly tothe right, and each top edge is aligned with the top edge of two otherblocks of conductive material in other second columns in the ascendingtrios; and the descending trios each comprise three sequential secondcolumns having blocks of conductive material with parallelogramfootprints, each parallelogram footprint having a top edge parallel to abottom edge, wherein the top and bottom edges of the parallelogram slopedownwardly to the right, and each top edge is aligned with the top edgeof two other blocks of conductive material in other second columns inthe descending trios.
 6. The integrated circuit of claim 5, wherein theslope of the top and bottom edges of the parallelogram footprints in theascending trios intersects with the slope of the top and bottom edges ofthe parallelogram footprints in the descending trios at an angle in therange of between 45 and 179 degrees.
 7. The integrated circuit of claim6, wherein the angle is about 130 degrees.
 8. The integrated circuit ofclaim 1, wherein the underlying active areas are oval shaped.
 9. Theintegrated circuit of claim 1, wherein the underlying active areascomprise one source region and two drain regions, and at least two wordlines contact the source region.
 10. The integrated circuit of claim 1,wherein the blocks of conductive material comprise cell contacts fromthe plurality of memory devices to the underlying active areas.
 11. Theintegrated circuit of claim 1, further comprising a plurality of bitlines overlying the active areas.
 12. An integrated circuit comprising:a plurality of substantially parallel first interconnect lines; aplurality of conductive plugs comprising, as seen in plan view, blocksof conductive material with a nonrectangular, parallelogram footprint,the blocks of conductive material flanked on a first pair of oppositesides by two of the interconnect lines and flanked on a second pair ofopposite sides by blocks of insulating material; a plurality of activeareas underlying the conductive plugs; and a plurality of drain regionsoverlying the plurality conductive plugs, wherein each of the blocks ofconductive material is configured to contact at least one of the activeareas and provide an electrical connection to at least one drain region.13. The integrated circuit of claim 12, wherein the blocks of connectivematerial comprise cell contacts.
 14. The integrated circuit of claim 12,wherein the first interconnect lines comprise word lines.
 15. Theintegrated circuit of claim 12, wherein the non-rectangular,parallelogram footprint is a rhomboid footprint.
 16. The integratedcircuit of claim 12, wherein the non-rectangular, parallelogramfootprint has at least two interior angles of between approximately 20and approximately 30 degrees.
 17. The integrated circuit of claim 12,wherein the non-rectangular, parallelogram footprint has at least twointerior angles of between approximately 40 and approximately 50degrees.
 18. The integrated circuit of claim 12, wherein the blocks ofconductive material are associated with a plan view pattern, the patterncomprising: first columns, each first column comprising one of the wordlines; second columns alternating regularly with the first columns, eachsecond column comprising the blocks of conductive material, whichalternate up and down each of the second columns with the blocks ofinsulating material, the second columns arranged in ascending anddescending trios, wherein: the ascending trios each comprise threesequential second columns having blocks of conductive material withparallelogram footprints, each parallelogram footprint having a top edgeparallel to a bottom edge, wherein the top and bottom edges of theparallelogram slope upwardly to the right, and each top edge is alignedwith the top edge of two other blocks of conductive material in othersecond columns in the ascending trios; and the descending trios eachcomprise three sequential second columns having blocks of conductivematerial with parallelogram footprints, each parallelogram footprinthaving a top edge parallel to a bottom edge, wherein the top and bottomedges of the parallelogram slope downwardly to the right, and each topedge is aligned with the top edge of two other blocks of conductivematerial in other second columns in the descending trios.
 19. Theintegrated circuit of claim 12, wherein the underlying active areas areoval shaped.
 20. The integrated circuit of claim 12, wherein theunderlying active areas comprise one source region and two drainregions, and at least two word lines contact the source region.